This invention generally relates to the art of electrical connectors and, particularly, to a connector having terminals with increased capacitance for controlling the impedance in the connector.
In today""s high speed electronic equipment, it is desirable that all components of an interconnection path be optimized for signal transmission characteristics, otherwise the integrity of the system will be impaired or degraded. Such characteristics include risetime degradation or system bandwidth, crosstalk, impedance control and propagation delay. Ideally, an electrical connector would have little or no affect on the interconnection system regarding these characteristics. An ideal connector would be xe2x80x9ctransparentxe2x80x9d. In other words, the system would function as if circuitry ran through the interconnection and there would be no effect on the system whatsoever. However, such an ideal connector is impractical or impossible, and continuous efforts are made to develop electrical connectors which have as little effect on the system as possible.
Impedance and inductance control are concerns in designing an ideal connector. This is particularly true in electrical connectors for high speed electronic equipment, i.e., involving high frequencies. As example of such connectors is the popular type of electrical connector commonly called an xe2x80x9cedge cardxe2x80x9d connector. An edge card connector is provided for receiving a printed circuit board or edge card having a mating edge and a plurality of contact pads adjacent the edge. Such edge connectors have an elongated housing defining an elongated receptacle or slot for receiving the mating edge of the printed circuit board. A plurality of terminals are spaced along one or both sides of the slot for engaging the contact pads adjacent the mating edge of the board. In many applications, such edge connectors are mounted on a second printed circuit board. The mating xe2x80x9cedgexe2x80x9d board commonly is called the xe2x80x9cdaughterboardxe2x80x9d, and the board to which the connector is mounted is called the xe2x80x9cmotherboardxe2x80x9d.
Another example of such connectors are board to board connectors in which a plug connector mounted on a board has an insertion portion with terminals thereon for insertion into a receptacle connector mounted on a board with terminals in a recess for receiving the insertion portion of the plug connector. The terminals in the plug connector mate with terminals in the receptacle connector to connect conductors on respective boards.
This invention is directed to an edge card connector wherein the terminals of the connector are structured to increase the capacitance thereof and, thereby, control the impedance of the connector. For instance, the connector may be interconnected in an electric circuit having a given impedance, and the terminals can be selected for tuning the connector to substantially match that impedance.
An object, therefore, of the invention is to provide a connector of the character described, with improved terminal structures for increasing the capacitance of the connector.
The connector is provided for use with a circuit component such as a card having an edge and a plurality of contact pads near the edge. A connector housing includes an elongated slot for receiving the edge of the circuit card therein and terminal cavities adjacent to the slot. A plurality of terminals are inserted into the terminal cavities. At least some of the terminals each includes a contact section extending into the slot for engaging a contact pad on the circuit card, along with an enlarged body section. A thin flexible contact arm extends between the body section and the contact section. A finger portion extends alongside the thin flexible contact arm to increase the capacitance of the terminal and, thereby, reduce the impedance of the circuit through the terminal.
In one embodiment of the invention, the finger portion is cantilevered alongside the thin flexible contact arm from a base of the finger portion integral with the arm. In another embodiment, the finger portion is cantilevered alongside the contact arm from a base of the finger portion integral with the contact section. In a further embodiment, the finger portion is integral with the contact arm at a point intermediate opposite ends of the finger portion, whereby the finger portion extends alongside the contact arm in opposite directions from that point.
The invention contemplates that at least one of the finger portions may be disposed on each of two opposite sides of the contact arm. A plurality of the finger portions may be disposed on one side of the contact arm. A plurality of the finger portions may be disposed on each of two opposite sides of the contact arm.
The invention also contemplates application to board to board connectors.
Other features of the terminal include a retention section projecting from the body section into a retention cavity in the housing. A tail section projects from the body section out of the housing for connection to an appropriate circuit trace on a printed circuit board. In the preferred embodiment of the invention, the aforementioned plurality of terminals are signal terminals which alternate along the slot with a plurality of ground terminals which also include finger portions facing the finger portions of the signal terminals longitudinally of the slot.
Other objects, features and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawings.